Recovering a profile that suddenly disappeared
From MozillaZine Knowledge Base
Thunderbird has a nasty habit of once in a great while forgetting about the existence of a profile if it uses the default name. When this occurs, you suddenly start up in the new account wizard and it looks like you lost everything. You haven't. It's just lost track of your profile, which is probably intact.
Another possibility is that your prefs.js file is empty or corrupt due to either Windows or Thunderbird crashing. Your prefs.js file has all of your account information and settings. In this case you haven't lost any of your mail or address books, but Thunderbird no longer knows how to fetch new mail or send messages, or display the folders in the folder pane. You'll need to recreate the accounts in Thunderbird unless you have a backup or unless it created a copy with a different name (for example, prefs-1.js).
Which problem do you have?
A quick way to tell which problem you're suffering from is to look at your personal address book within Thunderbird. If it looks okay, go to the Corrupt or empty prefs.js section. Otherwise, follow the instructions in the Lost profile section.
If Thunderbird didn't run the new account wizard when it started up, see Disappearing mail if some or all of your messages aren't visible in Thunderbird or see Empty folders if some of your folders are empty.
1. Follow the instructions on how to move a profile. This will tell Thunderbird again where your profile is stored.
2. Use the profile manager to change the name of your profile to a unique name to prevent this problem from occurring again.
That's it, you are done.
If this doesn't work:
If you run into problems don't spend too much time trying different ways to move your profile. Take a moment and confirm that your profile is still intact, and then consider whether it would be quicker to recover the data from the old profile than to keep trying to move it.
Is your profile intact?
Normally your profile is intact, and it just takes several tries to figure out how to move the profile. However, at some point you may want to do a sanity check that your profile is still intact. The easiest way is to open a console window (DOS box) and use a -profile "path" command line argument per this article to run Thunderbird using your profile. If that works then you know that your profile is okay, you just need to figure out whats causing your problem in moving the profile.
If that doesn't work (or you're not sure whether you made an error in using the command line arguments):
If you have your personal address book, your settings, and your inbox folders your profile is probably intact. You can either try to move the profile again, or migrate your data to a new profile per the next section. It's more work (you'll need to create the accounts again, re-install any extensions/themes you had added, and recreate any customizations you had made) but not as difficult.
Recovering data from your old profile
See Importing folders if you have problems installing the ImportExportTools extension. You probably left clicked on the download URL instead of right clicking and selecting "save link as".
Once things are working, read this article for how to recover the less important files.
Corrupt or empty prefs.js
A "empty" pref.js file typically isn't totally empty. It may have a few lines such as
or a couple dozen lines setting lots of unimportant preferences. Whats important is whether it still contains your account information, not how big it is.
Open the prefs.js file with a text editor such as Notepad (don't double click on it using Windows Explorer) and search for the string mail.account . It's used in statements such as user_pref("mail.account.account1.server", "server1") to define an account, and it's used in statements such as user_pref("mail.accountmanager.accounts", "account1, account2, account3") to list what accounts exists. If you can't find any, then your prefs.js file is either empty or corrupt.
1. Exit Thunderbird and make a backup copy of the prefs.js file.
2. Try to find a good copy of prefs.js that you can use to replace the bad one.
If you have a backup of your profile replace the "bad" prefs.js file with one from your backup. If you made your backup using Mozbackup you can unzip the "*.pcv" backup file as described here to get the backed up prefs.js file. Otherwise see if Thunderbird might have created a copy of your old prefs.js file using a slightly different filename such as prefs-1.js or prefs.bak. Check that it has account information before using it, you can't assume that it's a good copy just because it's larger. If it has account information, rename it to prefs.js and check whether its a read-only file. If so, change its file properties so that its writable. If you are using Windows you can do that by right clicking on the file in Windows Explorer, selecting Properties, clicking the General tab, unchecking the read-only checkbox, and pressing the OK button.
3. If you can't find a good copy of prefs.js try running CHKDSK to recover the file. You may be able to recover it in a C:\FOUND.000 directory. If you're using Linux or OSX try using fsck to recover the file.
4. Otherwise you will need to rebuild prefs.js. You can do this by creating the same accounts again in the existing profile and setting Thunderbird to use the local directories that still contain the missing mail, per this article. Another option is to create a new profile using the Profile Manager , create the accounts again, and then migrate your mail , address books, filters and other mail related files from the old profile per this article .
Once things are back to normal you might want to install the MailTweak extension. It has a preferences cache that will automatically restore prefs.js if your account settings disappear. However, thats no substitute for regularly backing up your profile.